Variable focus objective lens



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F. LAURENT July 9. 1968 VARIABLE] FOCUS OBJECTIVE LENS 2 Sheets-Sheet lFiled April 25, 1967 F1G.l.

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L 7 La L L10 L11 INVENTOR FRANcols LAURENT ATTORNEY July 9, 1968 I F.LAURENT VARIABLE FOCUS OBJECTIVE LENS 2 Sheets-$heet P.

Filed April 25. 1967 mm. FIEANQo/S' LAURENT ATTORNEY United StatesPatent 3,391,973 VARIABLE FOCUS OBJECTIVE LENS Francois Laurent,Yverdon, Vaud, Switzerland, assignor to Paillard S.A., Vaud,Switzerland, a corporation of Switzerland Continuation-impart ofapplication Ser. No. 322,339, Nov. 8, 1963. This application Apr. 25',1967, Ser. No. 633,516 Claims priority, application Switzerland, Nov.15, 1962, 13,370/ 62 1 Claim. (Cl. 350176) ABSTRACT OF THE DISCLOSURE Avariable focus objective lens of the type having mechanical compensationand by means of which it is possible to accomplish a focusing on anobject very close thereto, for example, an object situated at a distanceof a few centimeters therefrom, without any adjustment operation of thefocusing being accompanied by any modification in the exteriordimensions of the objective lens, having at least one fixed opticalelement disposed on the side towards the object, a second movabledivergent optical element, or variator element, a third movableconvergent optical element, or compensator element, and a fourth fixedconvergent element. The variation of the focal length is obtained by thedisplacement of the movable convergent optical element, or compensatorelement, and the compensation of the back focus to stabilize the imageis obtained by displacement of the movable divergent optical element, orvariator element, the first fixed element presenting a focal length atleast equal to the longest focal length of this objective lens,multiplied by k, k being the ratio of the longest focal length of theobjective lens divided by the shortest focal length, the focal length ofthe movable divergent optical element, or variator element, being atmost equal to 0.24 k multiplied by the longest focal length of theobjective lens, focusing being obtained by displacement of said movabledivergent optical element, or variator element. Said first fixed elementcan be convergent, divergent, or one having an infinite focal length.

This application is a continuation-in-part of Ser. No. 322,339, filedNov. 8, 1963, now abandoned.

The present invention concerns a variable focus objective lens of thetype having mechanical compensation and which comprises at least onefixed optical element, a first movable optical element as a variator anda second movable optical element as a compensator. The displacements ofthe first movable optical element with respect to the fixed elementpermit the variation in magnification of the objective lens, thisvariation causing a modification of the back focus of the objectivelens, i.e. of the length between the rear lens and the focal plane. Thedisplacement of the second movable optical element permits variation inthe back focus of the objective lens without sensibly modifying itsmagnification, so that by a judicious choice of simultaneousdisplacements of the first and second movable optical elements there canbe obtained a modification in the magnification of the objective lenswithout modifying the back focus thereof.

In known objective lenses of this type the adjustment of the focusing iseffected by varying the position of the front fixed element of theobjective lens, which element remains stationary during the variationsof the focal length. This frontal element presents a relatively longfocal length, so that it must effect a substantial displacement topermit the required focusing between infinity and the shortest focusingdistance. Therefore, there must be selected a compromise to avoid a toolarge variation in the exterior dimension of the objective lens duringthe variation of its focal length. For this reason, the shortest focallength is in general chosen around 1 m.

The object of the present invention is to provide an objective lens inwhich it is possible to effect a focusing on a very close object, forexample, situated at a distance of a few cm., without the adjustmentoperation of the focusing being accompanied by a modification in theexterior dimensions of the objective lens.

According to the present invention, a variable focus objective lensconsists of a first fixed element disposed on the side towards theobject, a second movable divergent element, a third movable convergentelement and a fourth fixed convergent element, in which the variation ofthe focal length is obtained by displacement of the movable convergentelement, the compensation of the back focus to stabilize the image beingobtained by displacement of the movable divergent element, characterizedin that the first fixed element presents a focal length at least equalto the longest focal length of the objective lens, multiplied by k, kbeing the ratio of the longest focal length of the objective lensdivided by the shortest focal length, the focal length of the movabledivergent element being at most equal to 0.24 k multiplied by thelongest focal length of the objective lens, focusing being obtained bythe displacement of the said movable divergent element.

The invention will now be described further, by way of example, withreference to the accompanying drawings, in which:

FIGURE 1 is an axial representation of the objective lens.

FIGURE 2 is a diagram showing the displacements of the variator and thecompensator as a function of the focal length chosen for the objectivelens.

FIGURE 3 shows the detail of the objective lenses.

FIGURE 4 shows in full line the aberration of sphericity and in dottedline the sine condition.

FIGURE 5 shows the astigmatism. The solid line indicates the tangentialcurvature, and the dotted line shows the sagittal curvature.

' FIGURES 4 and 5 refer to the objective when it is set for the shortfocal length of 9 mm.

The horizontal scale is: 1 cm. of the drawing corresponds to 0.1 mm.

The vertical scale is: 10 cm. for an angle of the ray of 18 degrees.

FIGURES 6 and 7 correspond to FIGURES 4 and 5 when the objective is seton the long focal length of 30 mm., wherein the vertical scale is: 10cm. for 5 degrees.

The objective lens shown comprises a first fixed frontal element 1, asecond divergent and movable element 2, a third convergent and movableelement 3, and a convergent fixed element 4. Each of these elements hasbeen shown as if it was constituted by a single lens, but it is quiteevident that in practice at least one of these elements must be formedby an assembly of several lenses, in such a manner as to permit thecorrection of the usual aberrations of objective lenses.

The focal length of the divergent element 2 is at the most equal to 0.24k multiplied by the longest focal length of the objective lens. Thefactor k represents the ratio of the longest to the shortest focallengths of the objective lens. In other terms k represents the number bywhich the shortest focal length must be multiplied to obtain the longestfocal length.

In the example described, the focal length of the objective lens canvary from 9 mm. to 33.44 mm. so that k equals 3.73. The focal length ofthe element 1 is at least equal to k multiplied by the longest focallength of the objective lens. Thus, in the objective lens represented,the focal length of the element 1 must at least be equal to l24.73 n1m.,this element being able to be convergent or divergent. In the exampleshown, the element 1 is convergent and presents a focal length of 340.78mm.

The focal length of the element 2 must be smaller than 0.24 k multipliedby 33.44 which equals 29.94 mm. The length chosen in the present case isequal to 28.3682

The movable convergent element presents a focal length of 19.63 mm. andthe fixed convergent element a focal length of 14 mm.

FIGURE 2 shows the position of the elements 2 and 3 as a function of thefocal length of the objective lens.

In the objective lens shown, the focusing is effected by a displacementof the divergent element 2, and as the refractive power of this elementis high, the displacements which must be effected to permit the focusingare very small.

In FIGURE 2, the curve 2'a shows the position which the element 2 mustoccupy as a function of the focal length when the focusing is adjustedon infinity, while the curve Z'b shows the position which the element 2must occupy for a focusing on 10 cm., and the curve 3' shows theposition which the element 3 must occupy with respect to the positionoccupied by the element 2.

Referring further to FIGURE 2, the axis of the abscissas is a lineargraduation. In a calculated example, the curve 2'a intersects the axisof the abscissas on a division corresponding to 45 mm. The divisioncorresponding to mm. coincides with the axis of the ordinates.

Due to the above-mentioned choice of refractive power of the elements 1and 2, it is possible to obtain a large variation of the ratio of thefocal lengths without upturning of the displacement of the element 2. Ifthis upturning is admitted, which is represented in broken lines inFIGURE 2. there can be obtained a very large total variation of theratios of the focal lengths. Finally, the focusing of the objective lenscan be extraordinarily close and it is possible to obtain a correctfocusing without exaggerated deformation of the object, when this isfound up to the immediate neighborhood of the ele ment 1.

The following is a table of values for all parameters of an operablelens according to the disclosure:

d, 111m. R; R; Glass 11 Spacing types L 2 +306. 4 00 SK 16 1. 62041 L 2+1201 +51. 03 SK 1. 02041 L 1. 5 189. 6 +33. 6 SK 16 1. 62041 L 1. 5+189. 6 +28.16 D 3128 1. 73150 2 L 4. 6 +128. 16 -28. 16 SK 16 1. 62410.1 L5 2. 5 +18. 28 +73. 14 LaK 9 1. 69100 P 7 co co BK7 1.52680 2: L13.0 +8. 6 13. 97 FK 6 1. 44628 0 L; 0.5 13. 97 +0. 72 L118]? 2 1.83739 55 Lo 0.6 7. 11 +20. 66 LaSF 2 1.83739 0 L 2. 5 +20. 66 --6. 9 SFS 3 1.78470 0.1 L 1.2 +1362 34 LaK 17 1.78847 0.1 L 2.6 +19.28 -4.87 LaK 17 1.78847 0 Ll3----- 0.5 4.87 +34.11 SP8 3 1.78470 Back focall0ngtl1=10.9589

rt thickness of the lens. R =Fr011t radius of curvature. R Roar radiusof curvature.

An important advantage of the objective lens is that its exteriordimensions are not modified during the adjustment of the focal length orof the focusing, as the distance between the fixed elements 1 and 4remains constant.

I claim:

1. A variable focus objective lens consisting of a first fixed componentdisposed on the side towards the object, a second movable divergentvariator component, a third movable convergent compensator component anda fourth fixed convergent component, in which the variation of the focallength is obtained by displacement of said movable convergentcompensator component for the compensation of the back focus of thisvariable focus objective lens to stabilize the image being obtained bythe displacement of the movable divergent variator component, the firstfixed component presenting a focal length at least equal to the longestfocal length of this objective lens, multiplied by k, It being the ratioof the longest focal length of this objective lens divided by theshortest focal length, the focal length of the movable divergentvariator component being at the most equal to 0.24 k multiplied by thelongest focal length of this objective lens, focusing 'being obtained bydisplacement of the said movable divergent variator component, wherebythe exterior dimensions of said lens are not modified during theadjustment of the focal length and of the focusing, said objective lenshaving substantially the following values: 1

11, mm. R1 R2 Glass 11 Spacing types Ll 2.5 +3004 00 sK10 1.02041 L2 2+1201 +5100 SK 10 1.02041 81 L0 15 -1s9.0 +330 SK 10 1.02041 L4 1.5+1300 +2s.10 D3128 1.13150 e2 L5 4.0 +2210 -22.10 SK 10 1.0241 0 L6 2.5+1s.2s +1214 LaKQ 1.09100 P... 1 55 BK7 1.52680 63 L1 5.0 +3.0 +1301 FK61.44628 Ls 0.5 -13.91 +0.12 LaSF2 1.83739 0 Lg 0.0 -1.11 +2000 LaSFZ1.03139 L10... 2.5 +2000 -09 SFSB 1.78470 0 L11-- 12 +1302 --34 LaK 111.78847 L12..." 10 +1020 -4.s1 LaK17 1.78847 11"... 05 -4.s1 +14.11 SFS31.78470 0 Back local length=10.9589

wherein the variable spacings e c and 2 have substantially the followingvalues:

wherein said first fixed component consists of lens L said secondcomponent consists of lenses L and L said third component consists oflenses L L and L P is a beam splitter with plain parallel sides, andsaid fourth component consists of lenses L L ,'L L L L and L Noreferences cited.

DAVID H. RUBIN, Primary Examiner.

JEWELI. H. PEDERSFN. Examiner.

R. J. STERN, Assistant Examiner.

